Field of the Invention
The present invention relates to a porous laminate, and more specifically, to a porous laminate in which a plurality of layers each containing polymer nanofibers are laminated.
Description of the Related Art
In recent years, a porous laminate, typified by a polymer nanofiber sheet, including a plurality of layers in which polymer nanofibers are accumulated and three-dimensionally entangled with each other has been attracting attention.
Unlike general fibers to be used for a nonwoven fabric or the like, one polymer nanofiber has a diameter of several microns or less. Therefore, a structural body formed of the polymer nanofibers is remarkably excellent as compared to a structural body formed of the general fibers in the point that a large specific surface area, a continuous pore structure of a nanosize, a low density, and the like are obtained, for example, when the polymer nanofibers are accumulated in a predetermined shape such as a sheet shape. With this, new functions such as mechanical strength, reactivity, electrical and optical characteristics, and permeability of an inside of a structural body can be imparted to the structural body formed of the polymer nanofibers. In particular, in the case of using a pore structure formed by accumulating the polymer nanofibers, a pore diameter of a submicron order can be obtained. In this respect, a structural member obtained by accumulating the polymer nanofibers is suitable for trapping and carrying fine particles. Further, the polymer nanofibers themselves are fibers each using an organic compound as a parent material, and hence are lightweight. Accordingly, the structural member obtained by accumulating the polymer nanofibers can be produced under a simple and inexpensive condition.
Incidentally, the structural member obtained by accumulating the polymer nanofibers utilizes the characteristics of the polymer nanofibers, and hence the structural member is used in a state of adhering to a support in most cases. In Japanese Patent Application Laid-Open No. 2005-538863, the above-mentioned structural member is used as an ink receiving layer by forming a layer formed of the polymer nanofibers on a surface of paper. Meanwhile, Japanese Patent Application Laid-Open No. 2012-219384 discloses a separator in which a nanofiber layer is bonded to a flexible base material such as paper. Japanese Patent Application Laid-Open No. 2012-219384 discloses that interfacial adhesiveness is enhanced by mixing nanobeads when bonding the base material and the nanofiber layer to each other.
However, a layer formed of the polymer nanofibers produced on a flexible support such as paper by the method disclosed in Japanese Patent Application Laid-Open No. 2005-538863 is delaminated from the support having the layer bonded thereto at an interface with respect to the support when a mechanical load such as a bending stress is applied to the support. As a result, the layer (polymer nanofiber layer) may be separated from the support. Meanwhile, although the procedure of Japanese Patent Application Laid-Open No. 2012-219384 can enhance the adhesiveness at the interface between the layer formed of the polymer nanofibers and the support, the nanobeads may clog a pore structure present in the layer formed of the polymer nanofibers. With this, a desired pore structure may not be obtained. Therefore, hitherto, a porous structural body having physical durability has not been obtained, which is not delaminated from the support even when a mechanical load such as a bending stress is applied to the support after production while maintaining the pore structure of the layer formed of the polymer nanofibers.
The present invention has been made so as to solve the above-mentioned problems, and it is an object of the present invention to provide a porous laminate having satisfactory resistance to a mechanical load such as a bending stress while maintaining the characteristics of a porous structure.